1. Field of the Invention
This invention relates, generally, to techniques for cleaning sludge deposits from oil storage tanks and, more particularly, to a chemical formulation and process of achieving the same. Specifically, the present invention relates to a chemical formulation for breaking the interfacial bonds between the various components of oil sludge and a process for utilizing the same.
2. Description of the Prior Art
In general, petroleum-containing sludges, hereafter referred to as oil sludges, are made up of three main constituents, that is water, petroleum and sludge solids. Such sludge solids include wax, tar, resins, biological material, metals and the like. The fuel oils used today differ from those used only a number of years ago in that the present refining processes demand the reprocessing of what was the formerly final products. Today's oil products are cracked at very high temperatures or pressures so as to obtain higher yields of the lighter distillates. The final residues or fuel oils, as the result of this treatment, contain compounds which are unstable. They separate as tar, gum, and the like combined with condensates to form sludge. Such oil sludges arise in petroleum production, as residual tanker sludge in transporting crude oil, as tank residues when storing the crude oil, and in the processing of crude oil.
The build up of oil sludge is a problem in that the referenced impurities of oil sludge interfere with the free-flow of oil and clog up fuel lines, screens and burner tips. Sludge builds up with each load of oil put into a tank and, if allowed to go unchecked, will result in poor atomization of fuel, reduction of storage tank capacity and eventual blockage of the tank's discharge lines. Such oil sludge wastes fuel, causes unnecessary shut down and reduces boiler efficiency.
As a result of this, oil tanks are periodically cleaned to repair leaks in the tank floor, steam coils, and roof drains. They are also cleaned to facilitate removal or repair of sunken roofs as well as to recover storage capacity and eliminate crude oil tank unit upsets. Crude oil unit upsets are generally caused by the pluggage of suction lines to the crude charge pumps, slugs of water due to pluggage of the tank water draw, or slugs of solids because of the high sludge levels in the tank. Additionally, clean storage tanks can be inspected and maintained to prevent any environmental damage.
Currently, there are two principal manners of cleaning tanks. The first is a mechanical cleaning program whereby agitation, movement and physical separation are typical components of the process. U.S. Pat. No. 2,065,462 discloses such a technique. Usually, the sludge must be removed from the tank before implementing a hydrocarbon recovery method. Removal presents quite an obstacle if the sludge is asphaltic, very compact or not fluid. Moreover, once the sludge is removed, it must still be treated to recover the hydrocarbons. External recovery systems include belt presses, hot pits, centrifuges and portable storage tanks which allow separation. These techniques, however, are generally not very efficient and do not recover all the hydrocarbons, leaving residual amounts in the solids which may classify them still as hazardous. Thus, hazardous waste disposal is reduced, but not eliminated. Mechanical methods can also impact tank integrity, thereby risking odor nuisances, vapor release and soil contamination.
A second primary technique for cleaning oil tanks involves a chemical method. Currently, Federal environmental laws regulating waste disposal provide incentive for efficient chemical methods for cleaning storage tank. U.S. Pat. No. 4,233,174, U.S. Pat. No. 4,417,976, U.S. Pat. No. 5,039,450 and U.S. Pat. No. 5,085,710 all disclose such techniques, while U.S. Pat. No. 4,293,348 and U.S. Pat. No. 5,031,648 relate to the chemical treatment of petroleum materials.
Many standard tank cleaning methods, however, are ineffective in minimizing wastes to meet Federal standards. These methods include manual removal of sludge by workers inside the tank, mechanical removal by front-end loader which necessitates cutting a hole in the tank's side for entry, removal by remote control dredging devices, removal by power spray nozzles and removal by circulating hot oil through the tank. In addition, as is indicated above, none of these methods in and of themselves recovers clean hydrocarbons from the sludge. To the contrary, the sludge, after it is removed, must be taken elsewhere for such hydrocarbon recovery.
Thus, while cleaning methods meeting Federal environmental regulations for the treatment of oil sludge have been devised, there is still a need for a chemical method which treats the oil sludge in situ by separating it into its major component parts, that is water, hydrocarbons and solid sludge residue, which in turn can be directed to their own separate storage tanks and uses. While such techniques may exist as indicated in the referenced patents, it is desired to accomplish this is a relatively short period of time to eliminate false readings, and such prior techniques require large tank down times to accomplish the cleaning.